WASHINGTON — One of the Senate’s most aggressive investigators is probing longtime Hillary Rodham Clinton aide Huma Abedin’s employment status, asking how she got a sweetheart deal to be a private six-figure consultant while still serving as a top State Department official.

Abedin, one of Clinton’s most loyal aides, is married to former Rep. Anthony Weiner, who’s in the midst of a vigorous effort to beat back his own scandal and become mayor.

The inquiry by Sen. Charles Grassley (R-Iowa), compiled in a three-page letter to Abedin and Secretary of State John Kerry, adds drama to Weiner’s bid.

Abedin has been essential to his attempt to move past his sexting scandal.

The couple hauled in as much as $350,000 in outside income on top of Abedin’s $135,000 government salary after Weiner quit Congress amid a sexting scandal when he got caught sending out Tweets of his crotch.

Abedin, who served as Clinton’s deputy chief of staff when Clinton was secretary of state, later became a “special government employee” who was able to haul in cash as a private contractor.

The change in status came to light only last month. Abedin took on the new assignment after she gave birth to son Jordan and began working from New York.

One of the clients she did consulting work for while on the government payroll was Teneo Holdings, a firm founded by longtime Bill Clinton aide Doug Band.

Grassley, the top Judiciary Committee Republican, wrote that he was concerned Abedin’s status “blurs the line between public- and private-sector employees, especially when employees receive full-time salaries for what appears to be part-time work.”

He peppered Abedin and Kerry with 13 questions about her employment. Among them: “Who authorized the change in status in your official title?” and “Who was made aware of the change in status?”

A State Department official, noted there were 100 such consultants at the agency, saying, “Miss Abedin’s status was approved through the normal process.”

The official couldn’t immediately answer who signed off on the consulting deal, saying Abedin submitted it to the ethics office in June of last year.

A person close to Abedin said she voluntarily disclosed that she worked for Hillary Clinton personally – “to allow Huma to begin planning for [Clinton’s] activities post-State,” as well as for the Clinton foundation and Teneo Holdings.

The person added that Teneo conducts “no business” with State and that Abedin “did not provide ‘political intelligence.’”

One source diagnosed the situation this way: “She has the Clinton disease. When your husband gets knocked down, get up right away or else.”

Grassley’s letter quotes from Teneo’s Web site, on which the firm calls itself the “next chapter in strategic advisory.”

“In what ways did the department interact with the companies for which you consulted?” the letter asks